Case Study: EP40 Used for Steel Bonding in Marine Applications

Overview

This case study by Master Bond Inc. evaluates the performance of EP40, a two-part, room temperature curing structural epoxy, for bonding naval steel in marine applications. EP40 is formulated for bonding, sealing, coating, and encapsulating with a 1:1 mix ratio and demonstrates strong adhesion to naval steel, a key material in shipbuilding.

With growing emphasis on reducing the environmental impact of shipping, researchers are exploring adhesive bonding to replace traditional welded and riveted joints, potentially enabling lighter, more fuel-efficient ships with lower emissions. However, adhesives face challenges due to aging from moisture, high temperatures, and UV exposure, which necessitates understanding their long-term behavior in marine environments.

The study by research centers CITENI and CITIC developed a novel methodology to characterize adhesive aging using EP40 on naval steel substrates. This comprehensive evaluation included single-lap shear tests, tensile adhesion tests on bonded joints, and bulk adhesive tests to assess mechanical, thermal, and chemical properties before and after accelerated aging in seawater.

Specimens were carefully prepared using aluminum molds per ASTM standards, ensuring controlled adhesive layer thickness and curing under pressure for over 72 hours at room temperature. Thermal analysis showed EP40’s stability up to ~294°C with no significant degradation, validating its suitability for typical marine temperature ranges. Mechanical testing revealed an average ultimate tensile strength of 14.36 MPa in bulk EP40 and 9.71 MPa in bonded steel joints, indicating strong bonding capability with predominantly cohesive failure within the epoxy layer.

Aging simulations involved immersing EP40-bonded joints in seawater under no load and under a constant load of 6% of tensile strength for extended durations (up to 522 hours). Results showed seawater absorption plateaued under 5%, following Fickian diffusion behavior. Although tensile strength decreased after aging, notably more under load, it remained above 4 MPa even after prolonged seawater exposure under load, demonstrating robust retention of mechanical integrity.

The authors concluded EP40 is a viable structural adhesive for marine environments, capable of maintaining performance under realistic aging conditions. The developed testing methodology using EP40 provides a reliable approach to evaluate marine adhesives, offering a valuable baseline for future studies aimed at replacing traditional shipbuilding joints with advanced adhesive technologies. This research supports the transition to lighter, more sustainable marine construction practices.

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